Apparatus and method for use in paging mode in wireless communications systems

ABSTRACT

Latency in receiving and detecting paging messages at a wireless terminal is reduced by employing a unique “super” paging time slot format. A paging super time slot includes a plurality of prescribed time slots. Each wireless terminal is associated with cyclically recurring super time slots. A super slot is associated with one or more wireless terminals. A base station always selects the first available time slot in a super time slot to transmit a paging message to a wireless terminal that is associated with the super time slot. Each wireless terminal monitors every time slot in the associated super time slot until either detecting reception of its associated paging message or detecting an empty time slot. In another embodiment of the invention, a unique partially overlapping super time slot format is employed in which a super time slot has at least one time slot common to its adjacent super time slots. This allows wireless terminals associated with adjacent super time slots to share the common at least one time slot. In turn, this results in balanced traffic loads, smoothed traffic fluctuation and reduced congestion.

RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/756,384, filed Jan. 8, 2001. U.S. patentapplication Ser. No. 09/774,311 and U.S. patent application Ser. No.09/756,370 were filed on Jan. 8, 2001.

TECHNICAL FIELD

[0002] This invention relates to wireless communications systems and,more particularly, to wireless communications between wireless terminalsand base stations.

BACKGROUND OF THE INVENTION

[0003] In wireless communications systems, wireless terminals canmaintain connectivity to a base station without actively communicatingwith the base station. Such wireless terminals are referred to as beingin a paging mode. In such a system, the wireless terminals (WTs) arepaged by associated base stations (BSs) to initiate communications. Inorder to realize this, the base stations typically have a channel on thedownlink called the paging channel. In prior known paging arrangements,the paging channel is subdivided into a plurality of paging time slots.A group of wireless terminals is typically allocated a paging time slotof a prescribed periodicity for receiving paging messages fromassociated base stations. As shown in FIG. 1, wireless terminals #1 and#2 are allocated to time slot A, wireless terminals #3 and #4 areallocated to time slot C, and so on. Each mobile unit is expected tomonitor for paging messages from an associated base station during thesepaging time slots. Thus, in the example shown in FIG. 1, wirelessterminal #1 and #2 only monitor time slots A and B, while wirelessterminals #3 and #4 only monitor time slots C and D, and so on. To thisend, the periodicity of the paging time slots is made sufficiently longthat the each of the wireless terminals can effectively turn off most ofits circuitry between two of its designated paging time slots and, thus,save energy. This is referred to as the wireless terminal entering aso-called “sleep” mode. The wireless terminal, even though in the sleepmode, still has to keep track of the received paging time slots. Thewireless terminal is caused to “wake up” prior to the arrival of itsdesignated paging time slot, tunes to the downlink channel and achievescarrier, timing and frame synchronization. Then, the wireless terminaldecodes the paging time slot and if its identifier is included in thewireless terminal's designated paging time slot, it knows that the pagemessage is meant for it. The wireless terminal then takes theappropriate action indicated in the paging message. If the pagingmessage is not meant for the wireless terminal, the wireless terminalreturns to the “sleep” mode, and monitors the next received paging timeslot designated to it.

[0004] As seen in FIG. 1, more than one wireless terminal shares thesame paging time slot. The rationale for this is that in general pagingmessages for a particular wireless terminal do not arrive very often,and paging messages for different wireless terminals arrive at mutuallyindependent time slots. Consequently, sharing of the so-called pagingtime slots among several wireless terminals is a more efficient way ofutilizing the paging channel. A problem of sharing of the paging timeslots among several wireless terminals, however, is that latency inreceiving a paging message is increased when several paging messagesarrive simultaneously for the wireless terminals sharing a particularpaging time slot. For example, consider that paging messages arrive intime slot A of FIG. 1 for both wireless terminals #1 and #2, then theassociated base station can only transmit one of the paging messages intime slot A, for example, the message for wireless terminal #1. Then,the base station must wait until time slot B to transmit the pagingmessage for wireless terminal #2. Depending on the arrival rates ofpaging messages and the number of wireless terminals sharing a pagingtime slot, the latency may become undesirably long.

SUMMARY OF THE INVENTION

[0005] Problems and limitations of prior wireless communications systemspaging arrangements are overcome, in one embodiment of the invention, byemploying a unique paging “super” time slot format. A paging super timeslot includes a plurality of prescribed time slots. Each wirelessterminal is associated with cyclically recurring super time slots. Asuper slot is associated with one or more wireless terminals.

[0006] A base station always selects the first available time slot in asuper time slot to transmit a paging message to a wireless terminal thatis associated with the super time slot. Each wireless terminal monitorsevery time slot in the associated super time slot until either detectingreception of its associated paging message or detecting an empty timeslot.

[0007] In another embodiment of the invention, a unique partiallyoverlapping super time slot format is employed in which a super timeslot has at least one time slot common to its adjacent super time slots.This allows wireless terminals associated with adjacent super time slotsto share the common at least one time slot. In turn, this results inbalanced traffic loads, smoothed traffic fluctuation and reducedcongestion.

[0008] A technical advantage of the invention is that latency in a basestation transmitting a paging message and, hence, in a wireless terminalreceiving a paging message is significantly reduced.

BRIEF DESCRIPTION OF THE DRAWING

[0009]FIG. 1 shows a prior art time slot format used to transmit pagingmessages in wireless communications systems;

[0010]FIG. 2 shows, in simplified block diagram form, a wirelessmultiple access communications system in which the invention may beadvantageously employed;

[0011]FIG. 3 shows a unique super time slot format in accordance withthe invention;

[0012]FIG. 4 also shows the unique super time slot format useful indescribing the invention;

[0013]FIG. 5 shows a unique partially overlapping super time slot formatin which adjacent super time slots have at least one time slot incommon;

[0014]FIG. 6 illustrates the unique non-overlapping super time slotformat of FIGS. 3 and 4 and its use in practicing the invention;

[0015]FIG. 7 illustrates the unique partially overlapping super timeslot format in which adjacent super time slots have at least one timeslot in common and its use in practicing the invention;

[0016]FIG. 8 is a flow chart illustrating steps in the process of awireless terminal receiving and responding to a paging message; and

[0017]FIG. 9 is a flow chart illustrating the steps in a process of abase station generating and transmitting paging messages to wirelessterminals.

DETAILED DESCRIPTION

[0018]FIG. 2 shows, in simplified block diagram form, a wirelessmultiple access communications system in which the invention may beadvantageously employed. It should be noted that although applicants'unique invention will be described in the context of a mobile wirelesscommunications system, it has equal application to non-mobile, e.g.fixed, wireless communications systems. One such mobile wirelesscommunications system is the Orthogonal Frequency Division Multiplexed(OFDM) based spread spectrum multiple access system.

[0019] Specifically, shown in FIG. 2 is a multiple access wirelesscommunications system 200. System 200 includes base station 201including antenna 202 and one or more remote wireless terminals, i.e.,wireless terminals 203-1, 203-2 through 203-Y including associatedantennas 204-1, 204-2 and 204-Y, respectively. Transmission of signalsis from and to base station 201, to and from remote wireless terminals203. All of wireless terminals 203 share the transmission spectrum in adynamic fashion.

[0020] In this example, base station 201 includes transmitter 205,receiver 207 and controller 206 for transmitting and receiving wirelessmessages via antenna 202. Controller 206 is employed to controloperation of transmitter 205 and receiver 207, in accordance with theinvention. Similarly, in this example, each of wireless terminals 203-1through 203-Y includes transmitter 208, receiver 210 and controller 209for transmitting and receiving wireless messages via antenna 204.Controller 209 is employed to control operation of transmitter 208 andreceiver 210, in accordance with the invention.

[0021] Base station 201 transmits paging messages to wireless terminals203. Typically, wireless terminals 203 when not in use are in a standbymode commonly referred to as a “sleep” mode. In the sleep mode most ofthe circuitry in the wireless terminal 203 is turned off in order toconserve energy and, thereby, extend battery life. In order for each ofthe wireless terminals 203 to detect whether there is a paging messageintended for it, the particular wireless terminal 203 must come out ofthe sleep mode, i.e., wake up, and monitor incoming time slots for anassociated paging message. As indicated above, FIG. 1 illustrates aprior time slot format for communication of paging messages between basestation 201 and wireless terminals 203. It is noted that since more thanone wireless terminal 203 can share a time slot, it is possible for morethan one paging message to arrive simultaneously for transmission towireless terminals 203. Since the base station 201 can only transmit onepaging message in a time slot, any additional paging messages must waitfor subsequent time slots to be transmitted. Depending on the number ofsimultaneously arriving paging messages and the number of wirelessterminals 203 sharing a time slot, delay in transmitting a particularpaging message can be significantly long.

[0022]FIG. 3 shows a unique super time slot format in accordance withthe invention that significantly reduces latency in the transmission andreception of paging messages. As shown in FIG. 3, a plurality ofprescribed time slots are grouped together into a super time slot, e.g.,time slots A1 and A2 into super time slot #1 and time slots A3 and A4into super time slot #2. These super time slots including appropriatepaging messages are formatted and transmitted by base station 201 towireless terminals 203. In this example, wireless terminals 203-1through 203-4 share super time slot #1. To this end, a paging message isgenerated by base station 201 and inserted into a time slot of a supertime slot associated with the current wireless terminal 203 intended tobe paged. It should be noted that any desired number of time slots maybe grouped into a super time slot and any desired number of super timeslots may be in a cycle of a cyclically repeating super time slotformat.

[0023] Note that by grouping time slots into super time slots, theprobability of congestion at all time slots of any super time slot issignificantly reduced because of statistical multiplexing. Consequently,the latency in a wireless terminal 203 receiving a paging message issignificantly reduced. However, the wireless terminals 203 are requiredto monitor more individual time slots, thereby increasing itscomputational effort.

[0024]FIG. 4 also shows the unique super time slot format useful indescribing the invention in reducing the wireless terminals 203computational effort. In order to reduce the computational effortrequired in wireless terminals in monitoring the super time slots forpaging messages, base station 201 and wireless terminals 203 follow aprescribed protocol when employing the super time slot format shown inFIG. 3. Specifically, base station 201 always employs the firstavailable time slot to transmit paging messages to the wirelessterminals 203. Each of wireless terminals 203 monitors its associatedsuper time slot for paging messages and abandons monitoring either uponreceiving a paging message directed to it or upon detecting an emptytime slot. An empty time slot is defined as one in which no pagingmessage has been transmitted.

[0025] The first available time slot for a paging message is theearliest time slot in a super slot associated with the intended wirelessterminal that base station 201 is able to transmit the paging message.By way of an example, wireless terminals 203-1 through 203-4 share supertime slot #1 which, in this example, includes time slots A1 and A2.Consider that in a current super time slot, base station 201 has apaging message to be sent to an intended wireless terminal 203-1. If intime slot A1, base station 201 has no other paging messages to betransmitted, base station 201, in accordance with the above-notedprotocol, transmits the paging message in time slot A1, which is thefirst available time slot for the current paging message. If there areother paging messages to be sent in time slot A1 as well, base station201 decides which paging message is to be sent in time slot A1. Forexample, if base station 201 decides to transmit the current pagingmessage for wireless terminal 203-1 in time slot A1, then time slot A1is the first available for the current paging message. Now if basestation 201 had decided to transmit another paging message in time slotA1, then time slot A2 may be the first available time slot to transportthe current paging message for wireless terminal 203-1. Furthermore, ifbase station 201 had decided to transmit other paging messages in timeslots A1 and A2 in the current super time slot, then the first availabletime slot for the paging message for the intended wireless terminal203-1 may be a time slot of the super time slot associated with wirelessterminal 203-1 in the next cycle of the format. In the above examples ofhaving more than one paging message to be sent to wireless terminals 203in a time slot common to the super time slots associated with thewireless terminals 203, the paging messages are contending for thesingle common time slot. The contention for the time slot could beresolved on a random basis. However, this is somewhat undesirable. Abetter solution is to resolve the contention by a specific fixed processto achieve better system performance, such as reducing latency oftransmitting paging messages. In accordance with the invention, aprocess is employed which allocates the common time slot to the pagingmessage intended for the wireless terminal 203 whose super time slot isearliest among all wireless terminals. The super time slot that isearliest is described below in relationship to step 905 of FIG. 9.

[0026] Now assuming that base station 201 has no paging message to betransmitted in super time slot #1, then there is no transmission of amessage in time slot A1 and the time slot is empty. Upon the associatedwireless terminals, e.g., 203-1 through 203-4, detecting that time slotA1 is empty, they stop monitoring time slot A2, thereby reducing thecomputational effort. In accordance with the invention, if base station201 has at least one paging message to be sent for wireless terminalsassociated with a super time slot, base station 201 never has an emptytime slot before a time slot in which paging messages are transported,so that wireless terminals 203-1 through 203-4, in this example, do notmiss any transmitted paging messages because of detecting an empty timeslot that precedes a time slot including a paging message.

[0027] It is noted that in the unique super time slot format of FIGS. 3and 4 congestion may occur at a super time slot because of fluctuationsin the paging message traffic. One possible technique for minimizingthis congestion is to use a super time slot having a larger number oftime slots. Unfortunately, use of more time slots in the super timeslots requires more computation in order to monitor the super time slotfor paging messages by the wireless terminals 203.

[0028]FIG. 5 shows a unique partially overlapping super time slot formatin which adjacent super time slots have at least one time slot incommon. Wireless terminals 203 monitor their associated super time slotsto detect paging messages. By way of an example, super time slot #1includes time slots A1 and A2, super time slot #2 includes time slots A2and A3, and so forth, and wireless terminals 203-1 and 203-2 share supertime slot #1, wireless terminals 203-3 and 203-4 share super time slot#2 and so forth. Consequently, in this example, time slot A2 in commonto both super time slot #1 and super time slot #2. Because of thispartially overlapping of time slots by the super time slots the pagingtraffic messages loads on the super time slots can be balanced, therebyreducing the probability of congestion at the super time slots.

[0029]FIG. 6 illustrates the unique non-overlapping super time slotformat of FIGS. 3 and 4, and its use in practicing the invention. Assumethat base station 201 has paging messages to be transmitted to wirelessterminals 203-1, 203-2, 203-3, 203-5 and 203-7. The paging messages forwireless terminals 203-1, 203-2, 203-5 and 203-7 are transmitted in timeslots A1, A2, A3 and A4, respectively. However, the paging message forwireless terminal 201-3 has to be transmitted in the next occurringsuper time slot #1 because of congestion in the current super time slot#1. Thus, it is seen that the paging message for wireless terminal 203-3is transmitted in the first available time slot in its associated supertime slot #1 that, in this example, is in the next super time slot cycleFIG. 7 illustrates the unique partially overlapping super time slotformat in which adjacent super time slots have at least one time slot incommon and its use in practicing the invention. Again, assume that basestation 201 has paging messages to be transmitted to wireless terminals203-1, 203-2, 203-3, 203-5 and 203-7. The paging messages for wirelessterminals 203-1, 203-2, 203-3, 203-5 and 203-7 are transmitted in timeslots A1, A2, A3, A4, and A5, respectively. Therefore, it is seen thatthe use of the unique partially overlapping super time slot formatresults in less latency in receiving and detecting the paging messagesin wireless terminals 203-1, 203-2, 203-3, 203-5 and 203-7.

[0030]FIG. 8 is a flow chart illustrating steps in the process of awireless terminal 203 receiving, detecting and responding to a pagingmessage. The process begins in the power saving mode, i.e., sleep mode,in step 801. Thereafter, step 802 tests to determine if a super timeslot timer has timed out. If the test result in step 802 is NO, step 802is repeated until it yields a YES result indicating the super time slottimer has timed out. The timing out of the super time slot timerindicates to the associated wireless terminal 203 that has to turn ON,i.e., wake up, in order to monitor its associated super time slot todetect if it has received any paging messages. Then, step 803 causes atime slot index for the current super time slot to be set to K=1. Step804 causes the associated wireless terminal 203 to decode any pagingmessage in time slot K of the super time slot. Step 805 tests todetermine if any decoded paging message is for the particular wirelessterminal 203. If the test result in step 805 is YES, the paging messageis for this particular wireless terminal 203 and step 806 causes theparticular wireless terminal 203 to respond. If the test result in step805 is NO, step 807 tests to determine if time slot K is empty or ifK≧N. N represents the number of time slots in a super slot. If the testresult in step 807 is NO, step 808 causes the wireless terminal 203 toset the time slot index to K=K+1, and then control is returned to step804 and appropriate ones of steps 804 through 808 are iterated untileither step 805 or step 807 yields a YES result. Again, if step 805yields a YES result, step 806 responds accordingly, as described above.If step 807 yields a YES result, step 809 resets the super time slottimer and control is returned to step 801, which causes the wirelessterminal 203 to enter the sleep mode. Thereafter, appropriate ones ofsteps 801 through 809 are iterated, as described above.

[0031]FIG. 9 is a flow chart illustrating the steps in a process of abase station 201 generating and transmitting paging messages to wirelessterminals 203. The process is begun in step 901 by base station 201generating a paging message for a particular intended wireless terminal203. Then, step 902 causes base station 201 to wait for the next supertime slot associated with the intended wireless terminal 203. This isrealized by step 903 testing to determine if a super time slot timer hastimed out. If the test result in step 903 is NO, step 903 is iterateduntil it yields a YES result. The YES result in step 903 indicated thata super time slot has arrived and step 904 causes base station 201 toset a time slot index for the current super time slot to K=1. Then, step905 tests to determine whether there is a paging message for anotherwireless terminal 203 having an associated super time slot prior intime, i.e., earlier, to the super time slot for the particular intendedwireless terminal 203. A super time slot is prior in time, i.e.,earlier, to another super time slot if the last time slot of the formersuper time slot precedes the last time slot of the latter super timeslot. Two super time slots are “contemporary” if their last time slotscompletely overlap. If the test result in step 905 is NO, step 906causes base station 201 to transmit the paging message to the particularintended wireless terminal 203. If the test result in step 905 is YES,step 907 causes base station 201 to transmit a paging message to theother wireless terminal 203 indicated in step 905. (Not shown in FIG. 9,if there is a paging message for another wireless terminal 203 having anassociated super time slot, which is contemporary with the super timeslot for the intended wireless terminal 203, base station 201 may chooseto transmit either of the paging messages on a random basis.)Thereafter, step 908 tests to determine whether time slot index K≧N. Nrepresents the number of time slots in a super slot. If the test resultin step 908 is NO, step 909 causes base station 201 to set the time slotindex to K=K+1 and control is returned to step 905. Thereafter,appropriate ones of steps 905 through 909 are iterated until either step905 yields a NO result or step 908 yields a YES result. If step 905yields a NO result, step 906 causes base station 201 to transmit thepaging message to the particular intended wireless terminal 203, asdescribed above. When step 908 yields a YES result, step 910 causes basestation 201 to rest the super time slot timer and control is returned tostep 902. Then, appropriate ones of steps 902 through 910 are iterated,as described above.

[0032] The above-described embodiments are, of course, merelyillustrative of the principles of the invention. Indeed, numerous othermethods or apparatus may be devised by those skilled in the art withoutdeparting from the spirit and scope of the invention. Moreover, theinvention may be implemented as hardware, as an integrated circuit, viaprogramming on a microprocessor, on a digital signal processor or thelike.

What is claimed is:
 1. Apparatus for use in a wireless terminal of awireless communications system to receive paging messages comprising: acontroller for controllably maintaining said wireless terminal in astandby mode of operation; a receiver for receiving a super time slotformat including a plurality cyclically recurring super time slots totransport paging messages to one or more wireless terminals, whereineach of said plurality of super time slots includes a plurality of timeslots, each time slot intended to transport a wireless terminal pagingmessage; and wherein said controller controllably causes said wirelessterminal to enter into a monitor mode for monitoring only the intervalof a received super time slot associated with said wireless terminal fora paging message intended for said wireless terminal and otherwisereturning to said standby mode of operation, wherein power consumptionis reduced.
 2. The apparatus as defined in claim 1 wherein saidcontroller determines whether said super time slot associated with saidwireless terminal includes a paging message intended for said wirelessterminal.
 3. The apparatus as defined in claim 2 wherein said wirelessterminal includes a transmitter and said controller controls saidwireless terminal to transmit a paging response message via saidtransmitter when it is determined that said super time slot associatedwith said wireless terminal includes a paging message intended for saidwireless terminal.
 4. The apparatus as defined in claim 3 wherein saidcontroller causes said wireless terminal to enter said standby mode whenit is determined that said super time slot does not include a pagingmessage intended for said wireless terminal.
 5. The apparatus as definedin claim 2 wherein said controller is equipped to determine when a timeslot in said super time slot does not include any message and furthercauses said wireless terminal to be in said standby mode upon detectingthat at least one time slot does not include a message.
 6. A method foruse in a wireless terminal of a wireless communications system toreceive paging messages comprising the steps of: maintaining saidwireless terminal in a standby mode of operation; receiving a super timeslot format including a plurality of cyclically recurring super timeslots to transport paging messages to one or more wireless terminals,wherein each of said plurality of super time slots includes a pluralityof time slots, each time slot intended to transport a wireless terminalpaging message; and monitoring only the interval of a received supertime slot associated with said wireless terminal for a paging messageintended for said wireless terminal and otherwise returning to saidstandby mode of operation, wherein power consumption is reduced.
 7. Themethod as defined in claim 6 wherein said step of monitoring includes astep of determining whether said super time slot associated with saidwireless terminal includes a paging message intended for said wirelessterminal.
 8. The method as defined in claim 7 further including a stepof transmitting a paging response message when it is determined thatsaid super time slot associated with said wireless terminal includes apaging message intended for said wireless terminal.
 9. The method asdefined in claim 7 further including a step of causing said wirelessterminal to enter said standby mode when it is determined that saidsuper time slot does not include a paging message intended for saidwireless terminal.
 10. The method as defined in claim 7 wherein saidstep of monitoring includes a step of determining when a time slot insaid super time slot does not include any message and further causessaid wireless terminal to be in said standby mode upon detecting that atleast no time slot does not include a message.
 11. Apparatus for use ina wireless terminal of a wireless communications system to receivepaging messages comprising: means for controllably maintaining saidwireless terminal in a standby mode of operation; means for receiving asuper time slot format including a plurality of cyclically recurringsuper time slots to transport paging messages to one or more wirelessterminals, wherein each of said plurality of super time slots includes aplurality of time slots, each time slot intended to transport a wirelessterminal paging message; and means for monitoring only the interval of areceived super time slot associated with said wireless terminal for apaging message intended for said wireless terminal, wherein powerconsumption is reduced.